Evolution of the Jurassic Comallo volcanic sedimentary complex in the western North Patagonian Massif, Rio Negro province, Argentina

BENEDINI, LEONARDO; PAVON PIVETTA, CECILIA; GREGORI, DANIEL; STRAZZERE, LEONARDO; BARROS, MERCEDES; MARCOS, PAULO; GERALDES, MAURO

INTERNATIONAL GEOLOGY REVIEW

TAYLOR & FRANCIS INC

Año: 2020 p. 1 - 23

0020-6814

Here we define the Comallo volcanic sedimentary complex of the western North PatagonianMassif. It is composed by two members that include 9 lithofacies and 7 facies associations.The lower member is represented by massive and stratified lapilli tuffs, lithic and tuffaceousbreccias, coherent andesite-dacite lava-flows, andesitic breccias, and massive crystalline limestones.The upper member consists of red conglomerates, parallel and cross-stratificationsandstones, and mudstones. The lower member is interpreted as having been deposited bydilute and dense pyroclastic currents, block and ash deposits and lava-flow, and hypersalinelacustrine environments. The upper member is considered to have been deposited in fluviatileenvironments. A new U-Pb age of 192.0 ± 3.0 Ma (Sinemurian) was obtained for thiscomplex. It is coeval with several volcanic sedimentary units that crop out along the westernNorth Patagonian Massif, the Neuquén basin and the Extraandean Chubut in pull-apart or riftdepocentres. The movements of the NW-SE strike-slip faults that border the northern andsouthern limits of the Comallo depocentre made possible the development of a pull-apartbasin as well as the volcanism and the fluvial system. This and other coeval units weredeposited in similar environmental conditions along the North Patagonian Massif, theNeuquén basin and the extraandean Chubut, indicating a similar tectonomagmatic setting,in a tensional rear-arc during Lower Jurassic times.